The present invention generally relates to the removal of copper ions from copper ore, and more particularly to a multi-phase copper ion removal method using organic extractants in which the extractants are purified during use. This process improves the level of extractant efficiency and operating capabilities of the system.
The overall efficiency of a copper mining operation depends on the techniques which are used to remove copper from raw ore. Many different methods have been developed over time to accomplish copper removal with a maximum degree of effectiveness. Of primary interest are various techniques which are collectively known as "copper hydrometallurgy" in which copper ions are leached or otherwise extracted from raw ore using chemical agents. According to Arbiter, N., et al., "Copper Hydrometallurgy--Evolution and Milestones", Mining Engineering, February 1984 (pp. 118-123) which is incorporated herein by reference, copper hydrometallurgy techniques have been of interest since as early as the 17th century when copper recovery methods involving iron precipitating agents were tested. Other removal agents were tested and analyzed in later years, including H.sub.2 S (hydrogen sulfide) which was used to precipitate CuS (copper sulfide) from copper ore in the late 1800s and early 1900s.
During the early 20th century, further developments were made in copper extraction technology. For example, ammonia and ferric sulfate leaching processes were tested extensively during the 1930s in combination with a further procedure known as "electrowinning". Electrowinning basically involves a process in which a metal ion-containing solution is placed in contact with at least one cathode and anode, followed by the application of electricity to the solution. As a result, metal (e.g. copper) ions within the solution are plated onto the cathode and thereafter removed in elemental form. Electrowinning as an electrochemical recovery process is known in the art and discussed in a number of literature references, including Krishman, E. R. et al., Recovery of Metals from Sludges and Wastewaters, Noyes Data Corporation, New Jersey, pp. 38-46 (1993) which is likewise incorporated herein by reference.
In the 1950s and 1960s, a different type of extractant was developed which offered considerable promise in copper recovery processes. As discussed in "Solvent Extraction Boom in Latin America", Engineering and Mining Journal, December 1994 (pp. 18-21) which is also incorporated herein by reference, organic solvent materials (hereinafter "organic extractants") were produced and successfully tested. These materials enabled the efficient extraction of copper ions in a multi-stage chemical process. Organic extractants were initially designed for uranium recovery, but were later demonstrated to function effectively in the extraction of copper. Organic extractants are specifically employed after the application of an initial leaching solution (hereinafter designated as a "lixivant solution") to copper ore materials. This step generates a lixivant product containing copper ions therein. The organic extractants are then used to "extract" and remove copper ions from the lixivant product to generate a copper ion-rich organic solution. As discussed further below, many different organic extractants may be obtained from a variety of commercial sources including the Henkel Corporation (Mineral Industry Division) of Tucson, Ariz. (which markets organic extractants under the names "LIX.RTM.-65", "LIX.RTM.-84", "LIX.RTM.-860" and others), and Acorga Ltd. which likewise markets extractants under the name PT.50. Organic extractants sold under these designations which are of primary interest in this case consist of hydroxyphenyl oximes having the following basic chemical formula: (C.sub.6 H.sub.3)(R)(OH)CNOHR.sub.1 [R=C.sub.9 H.sub.19 or C.sub.12 H.sub.25 ; and R.sub.1 =H, CH.sub.3, or C.sub.6 H.sub.5 ]. This structure is illustrated as follows: ##STR1## Other compositions (which are commercially available from the Henkel Corporation (Mineral Industry Division) of Tucson, Ariz. include: (1) "LIX.RTM.-622N" [5-nonylsalicylaldoxime]; (2) "LIX.RTM.-984N [a mixture of 2-hydroxy-5-nonyl-acetophenone oxime and 5-nonylsalicylaldoxime]; (3) "LIX.RTM.-54" [C.sub.6 H.sub.5 COCH.sub.2 C.sub.7 H.sub.15 ]; and (4) "LIX.RTM.-63" which has the following structure: ##STR2## These materials are currently being used on a large-scale basis in many different countries. In particular, they form an essential part of a basic process known as "SX/EW". The term "SX/EW" stands for "solvent extraction/electrowinning", with the term "electrowinning" being defined above. To illustrate the manner in which organic extractants are used in this procedure, the following basic steps summarize the SX/EW process:
(1) An initial lixivant is first selected for use in leaching copper ions from copper ore. Many different lixivants may be employed for this purpose. Representative lixivants include but are not limited to sulfuric acid (H.sub.2 SO.sub.4); a combination of H.sub.2 SO.sub.4 and Fe.sub.2 (SO.sub.4).sub.3 (primarily for sulfide-containing ore materials); acidic chloride solutions (e.g. ferric chloride [FeCl.sub.2 ] or cupric chloride [CuCl]); nitrate solutions; ammonia, and ammonium salt compositions.
(2) The selected lixivant is then applied to the ore, with the lixivant being allowed to percolate downwardly into the ore. As a result, copper ions are leached from the ore and collected within the lixivant to generate a lixivant product which consists of a copper ion concentrate (also known as a "pregnant leach solution"). Further detailed information regarding the lixivant leaching process is disclosed in U.S. Pat. No. 5,476,591 to Green et al. which is incorporated herein by reference.
(3) The lixivant product/copper ion concentrate is thereafter combined (e.g. mixed) with a selected organic extractant as described above. Preferred compositions for this purpose will again consist of hydroxyphenyl oximes having the following basic chemical formula: (C.sub.6 H.sub.3)(R)(OH)CNOHR.sub.1 [R=C.sub.9 H.sub.19 or C.sub.12 H.sub.25 ; and R.sub.1 =H, CH.sub.3, or C.sub.6 H.sub.5 ]. Commercially-available organic extractant compositions (including the materials listed above) typically consist of a mixture containing about 90-95% of a petroleum dilutant (e.g. kerosene or tridecanol) and about 5-10% hydroxyphenyl oxime. Prior to combination of the organic extractant and the lixivant product, the organic extractant will contain little or no copper ions therein (depending on whether a fresh or recycled extractant supply is involved) and is also known as a "barren organic extractant". During the mixture of these components, copper ions within the lixivant product are transferred directly into the barren organic extractant. As a result, a first organic phase is produced (which consists of a "loaded organic extractant" containing copper ions from the lixivant product) and a first aqueous phase (also known as the "raffinate") which consists of the lixivant solution which lacks any substantial or appreciable amounts of dissolved copper therein. Both the first aqueous phase and the first organic phase spontaneously separate into discrete layers based on substantial differences in polarity and other physical factors. The first aqueous phase (e.g. the raffinate) is either discarded, stored for future use, or immediately reused on additional amounts of ore. The first organic phase is retained for further processing in accordance with the steps described below.
At this stage, it should be noted that the initial lixivant product (e.g. the pregnant leach solution) prior to treatment with the organic extractant will typically have a significant amount of solid waste material therein. This waste material (which may include fine dirt, sand, rock dust, vegetable matter, mineral residue, miscellaneous suspended solids, and the like) typically comes from raw ore or other sources. Since, in conventional SX/EW processes, the lixivant product is stored outdoors in a large "pond-type" open area environment, solid waste matter may be transferred into the lixivant product by wind, rain, and other environmental forces. The presence of these materials in the lixivant product can reduce the operating efficiency of the system at this stage and in subsequent stages. For example, the existence of solid waste matter carried over into the various phases of the SX/EW treatment system can result in increased phase separation time and/or incomplete phase separation. A lack of complete phase separation can likewise cause a significant amount of the organic extractant to remain within the treated lixivant solution or other aqueous phases generated during treatment. In this regard, considerable losses of the expensive organic extractant can occur. As discussed further below, the present invention is designed to avoid these problems so that a more economical and efficient copper extraction process can take place.
(4) The first organic phase (e.g. the "loaded organic extractant") is then placed in direct physical contact (mixed) with an electrolyte solution (which, at this stage, is also known as a "lean electrolyte solution"). Representative electrolyte solutions include an aqueous sulfuric acid (H.sub.2 SO.sub.4) solution which will contain about 80-95% by weight water, about 5-20% by weight sulfuric acid, and about 0-0.5% by weight cobalt (in the form of cobalt oxide or metallic cobalt powder) which (if used) is designed to control anode losses and improve cathode plating in the electrowinning stages of the system. Other representative electrolyte solutions include but are not limited to strong acid materials such as HCl which are selected in accordance with preliminary tests on the materials being treated. When these materials are combined, the desired copper ions from the loaded organic extractant are transferred into the electrolyte solution with the corresponding creation of a second organic phase and a second aqueous phase. The second organic phase will consist of the original organic extractant which lacks any substantial or appreciable amounts of copper ions therein (again conventionally known at this stage as the "barren organic extractant"). In contrast, the second aqueous phase (also known as the "rich electrolyte") will consist of the electrolyte solution containing the copper ions transferred from the first organic phase. The second organic phase can thereafter be routed back to subsequent portions of the system for reuse in treating additional copper-containing lixivant materials. However, the presence of extraneous solid waste matter within both phases at this stage will again result in (1) increased phase separation time; and (2) incomplete phase separation which can cause significant amounts of the organic extractant to remain within the second aqueous phase (e.g. the rich electrolyte). Both of these problems further increase the losses of valuable organic extractant materials and generally diminish the operating efficiency of the entire copper processing system.
(5) Finally, the second aqueous phase (which contains the desired copper ions and is again characterized as the "rich electrolyte") is transferred into a conventional electrowinning system. Within the electrowinning system, the second aqueous phase is placed in contact with at least one cathode and at least one anode, followed by the application of electricity to the electrolyte. This process causes copper from the second aqueous phase to be plated onto the cathode in elemental form, thereby completing the copper recovery process. However, the presence of extraneous solid waste material in the second aqueous phase (e.g. the rich electrolyte) at this stage can adversely interfere with the electrowinning process. Solid materials within the rich electrolyte will result in decreased current efficiency within the system and a reduction in purity of the plated copper product caused by the presence of suspended contaminants including dirt, grease, and other comparable materials.
As described above, the presence of suspended contaminants within an SX/EW system can cause considerable problems and economic losses. Once these materials enter the system at any stage (especially during the initial ore treatment step), they will typically remain within all of the subsequently-formed phases (both organic and aqueous). It is therefore important to remove these contaminants from the system as completely as possible. The present invention solves this problem in a highly effective manner with a minimal number of process steps and equipment. As a result, numerous benefits are achieved including a considerable reduction in the amount of organic extractant which is lost during the various stages of the production process, a decrease in processing time, and more effective electrowinning. The present invention therefore satisfies a long-felt need in the copper processing industry as discussed